The present invention relates to a panoramic ion detector, which can be used for the detection of charged particles, particularly in mass spectrography.
French Patent Application No. EN 77 35185 of Nov. 23rd 1977 in the name of the present Applicant, describes a panoramic ion detector which converts ions into electrons, whilst maintaining the same spatial distribution for the electron beams formed as for the ion beams to be analysed.
This type of detector comprises a diaphragm with plane symmetry brought to earth potential and having an opening permitting the passage of ion beams, an electrode for converting ions into electrons and having an opening facing the opening of the diaphragm, said conversion electrode having a plane symmetry and brought to a negative potential compared with earth potential and a plane electrode facing the conversion electrode and brought to a positive potential compared with the potential of the conversion electrode.
This type of detector is intended to operate in numerous cases in the presence of a magnetic field and in particular a magnetic stray field of the magnetic deviation and focusing sector of a mass spectrography. Whereas the ion beams are relatively little disturbed in their geometrical configuration by the presence of this magnetic field, the secondary electrons emitted by the conversion electrode are extremely sensitive to this field. They have a tendency to spread along divergent paths and the distribution of the secondary electron beams resulting from the incident ion beams corresponds very poorly with that of the ion beams, which is a major disadvantage in a mass spectrometer with separation of the masses by magnetic field.
To obviate this disadvantage, the invention according to the above-mentioned French Patent Application proposed giving the conversion electrode and more specifically downstream face thereof an appropriate shape. As a result of this concave shape in which the surface of the electrode is substantially perpendicular to the magnetic field lines, the dispersions of the dispersions of the electron paths are minimised and the distribution of the electron beams substantially corresponds to that of the ion beams.